Electrical power distribution systems often include overhead electrical power distribution lines mounted upon poles by a wide variety of mounting structure. Other distribution systems include underground distribution lines in which protected cables run under the ground surface. It is often necessary to take phase-to-phase or phase-to-ground voltage measurements across distribution and transmission lines while testing for induced or live power line or equipment.
Known high voltage safety line detectors, meters and testers comprise high resistance probes connected in series with a calibrated panel meter to read the voltage across the phase-to-phase or phase-to-ground terminals. They are designed for use as safety tools by high voltage line maintenance workers to verify the status of the line or equipment as nominal, induced or de-energized voltage. Known devices for providing such measurements include contact type and non-contact type. With contact type a reference probe or transmitter and a meter probe or receiver are connected in series with a cable as the loop is closed with load terminals.
The high resistance probes include a high voltage resistor connected in series with an electrode. The voltage distribution along the length of the high voltage resistor is non-uniform due to stray capacitance. This can result in errors in voltage measurement and provide unequal electrical stress distribution along the high voltage resistor.
Particularly, the high voltage measurement is carried out by using high voltage resistors in the phasing meter. One type of phasing meter uses a micro ammeter method of measurement. The voltage applied across the resistor leads to current flow in a meter circuit and amount of current flow corresponds to the voltage being measured. Another method is known as the voltage divider method and the phasing meter includes high value resistors producing a high voltage drop and a low value resistor producing a low voltage drop. The line to line or line to ground high voltage is applied across the resistors which are in series and the voltage drop across the low value resistor corresponds to the actual voltage being measured.
A high voltage resistor used in a phasing meter may have a non-uniform voltage distribution along the length of the resistor and creates instability due to stray capacitance between resistance portions to ground. The voltage stress is not uniform across the length of the resistor due to stray capacitance. The voltage stress will be more than two times the uniform stress at the resistor end near to the high voltage side. This leads to degradation of the resistor material at these points. Also, due to stray capacitance, the current which is flowing through the circuit is not the same as the theoretically calculated current leading to voltage measurement errors. The total current should be the circuit and stray capacitive current. However, the actual current portion is diverted by the stray capacitance leading to the measurement error.
The disclosure is directed to improvements in high voltage phasing voltmeters.